Device for electric precipitator

ABSTRACT

A device for electric precipitators designed for horizontal gas flow and having plane precipitation electrodes in a number of rows parallel to the direction of gas flow and with emission electrodes situated between said rows, and equipped with an impact device for cleaning at specific intervals the precipitation electrodes, the rows of precipitation electrodes being situated between a number of transverse bars at different heights of the precipitator, said bars having guides opposite each row of precipitation electrodes, said electrodes in each row being linked together and the impact device being designed in known manner to strike against the rows of linked precipitation electrodes to displace them one after the other in the plane of each row.

United States Patent [1 1 [111 3,748,831 Lagerdahl et a1. July 31, 1973[5 DEVICE FOR ELECTRIC PRECIPITATOR 2,812,035 11 1957 Sohlman et al 55130 x Inventors: Sebastian Lagerdahl, Greenwich;

Kenneth Mascord, Sidney, both of Australia; Sten Maartmann, Klinten,Sweden Aktiebolaget Svenska Flaktfabriken, Nacka, Sweden Filed: June 3,1971 Appl. No.: 149,625

Assignee:

References Cited UNITED STATES PATENTS 2/1945 Hedberg et al. 55/130 X12/1950 Schmidt 55/154 X Primary ExaminerDennis E. Talbert, Jr.Att0rneyH0ws0n & Howson [57] ABSTRACT A device for electricprecipitators designed for horizontal gas flow and having planeprecipitation electrodes in a number of rows parallel to the directionof gas flow and with emission electrodes situated between said rows, andequipped with an impact device for cleaning at specific intervals theprecipitation electrodes, the rows of precipitation electrodes beingsituated between a number of transverse bars at different heights of theprecipitator, said bars having guides opposite each row of precipitationelectrodes, said electrodes in each row being linked together and theimpact device being designed in known manner to strike against the rowsof linked precipitation electrodes to displace them one after the otherin the plane of each row.

9 Claims, 5 Drawing Figures PATENIEDJUL31 3,748.83 1

SHEEI 1 0F 4 Fig. 7

PAIENIEDJMHW 3.748.831

SHEEI 2 or 4 DEVICE FOR ELECTRIC PRECIPITATOR This invention relates toa device for use with electric precipitators designed for horizontalflow of the gas to be cleaned and having plane precipitation electrodesplaced in a number of parallel rows, with emission electrodes situatedbetween the rows, and equipped with hammers or similar impact devicesfor cleaning of the precipitation electrodes at specific intervals.

In view of its ability to separate difficultly separated dust particlesfrom flue-gases an electric precipitator is generally used whenenvironmental hygiene requires degress of separation of an order of 98percent and above. In electric precipitators of dry type the dustparticles are separated from the gas flow by electrical charging of theparticles with electrons emitted by emission electrodes and byattraction of the particles to grounded precipitation electrodes underthe influence of the strength of the electro-static field. One of themost significant problems in the design and operation of an electricprecipitator of this type is the removal of the precipitated materialfrom the precipitation electrodes without the material being carriedalong once again by the gas flow. The commonest method for this purposeis to shake the precipitation electrodes, and in some cases also theemission electrodes, by blows upon them at specific intervals, by meansof which the material is removed and collected in dust traps and carriedoff, for example, by means of screw conveyors or similar mechanicalelement. From the economic aspect it is often necessary to designelectric precipitators of considerable height, and consequently withlarge height of electrodes, e.g., m or more.

A common design of electric precipitator comprises plane, stiffenedprecipitation electrodes arranged in a number of parallel rows ofseveral electrode surfaces placed one after the other. Electricprecipitators of this size are designed for high nominal gas speedshaving regard to the available space. Severe problems often arise insuch cases as a result of violent turbulence of the incoming gas which,after passage through the gas distributor screens on the inlet side,readily sets up oscillations of a standing sine wave character in theprecipitation electrode plates. The oscillations result in a reductionof the so called electrical voltage distance in the electricprecipitator causing recurrent flashover and other interruptions ofoperation, for which reason it is extremely urgent to remedy thisdisadvantage, which is disastrous for the reliability of operation.These oscillations arise despite the fact that the precipitationelectrode plates are usually stiffened by bending back of their fore andrear side-edges. The attempt has been made to limit the oscillations ofthe precipitation electrodes by placing two plate bands on the two sidesof the cross-sectional profile of the precipitation electrodes atroughly half the height of the electric precipitator. This has theserious disadvantage, however, of reducing also the aforesaid voltagedistance, so that the operating voltage of the electric precipitatormust be somewhat reduced. This reduction of the operating voltage,however, results in a heavy reduction of the efficiency of the electricprecipitator, for which reason the separation per volume of precipitatoris smaller and the precipitator is consequently uneconomical inoperation. This design also has the disadvantage that the impact energyfrom the impact device cannot be fully utilized for shaking down of theparticles collected on the precipitation electrodes.

The object of the invention is to provide a device for controlling themovement of the precipitation electrodes during hammer-cleaning, so thatthis can be done at the normal operating voltage of the electricprecipitator and at the same time the oscillations of the precipitationelectrodes and their movement relative to one another can be kept undercontrol, so that the electrical voltage distance in the electricprecipitator can be kept at an optimal value, with the best possibleefficiency in consequence. The device is characterized in that theparallel rows of precipitation electrodes are situated between a numberof transverse bars disposed at different heights in the electricprecipitator and across it perpendicular to the plane through the saidrows of precipitation electrodes, which bars have guides opposite eachrow of precipitation electrodes. Furthermore the precipitationelectrodes in each row are linked together in the direction of impactalong the plane for the impact device and In addition, the impact deviceis designed in the known manner to strike against the rows ofprecipitation electrodes so as to displace the electrodes one after theother. An effective embodiment in which each precipitation electrode hasa fore and rear side-edge partially bent back in the flow direction ofthe gas for stiffening of the electrode and a plane intermediateportion, is characterized in that the precipitation electrodes in eachrow are linked together by means of tongues secured preferentially in arear, bentback side-edge and entering preferentially into a fore,bent-back side-edge of the next precipitation electrode, and in that theforemost bent-back side-edge and the last bent-back side-edge in eachrow are held rigidly laterally to the said aforementioned transversebars by means of a guide attached to each bar. Each tongue can be of lshape, i.e., with a bent-up lip to permit a limited reciprocal movement,at the same time preventing exceeding of said movement and involuntaryseparation of two adjacent precipitation electrodes from one another.According to another embodiment all precipitation electrodes in one rowcan be anchored to one another by means of a continuous long and narrow,flat (placed edgeways) metal band passing both through the fore and rearbent-back side-edge of each precipitation electrode. This band maysuitably be fixed to one of said bars and passed through the other barin a clearance hole, so assuring a limited reciprocal movementlongitudinally but at the same time to prevent exceeding of thismovement and involuntary separation of two adjacent precipitationelectrodes from one another. In an improvement of this embodiment theband has a number of cut-outs or notcheflmnalong one edge resting in thelower edge of the non-threaded opening, the which cut-outs or notchespermit a limited reciprocal movement longitudinally but at the same timeprevent exceeding of said involuntary movement and separation of twoadjacent precipitation electrodes from one another, which duringoperation of the precipitator must be considered as virtually acatastrophy. A further embodiment of the device according to theinvention is characterized in that, in each row, the precipitationelectrodes are anchored to one another by means of a li-shaped strapattached to the rear bentback side-edge, and embracing the forebent-back sideedge of the next precipitation electrode, and in that thefront bent-back side-edge and the last bent-back sideedge in each rowviewed in the direction of flow of the gas are held fixed laterally tosaid bars by means of said guides, preferentially designed as a l:shapedor j-shaped strap attached to each bar. An advantageous embodiment ofthe new and improved device is characterized in that the two opposingsides of the horizontal beams holding together the side-walls of theelectric precipitator carry tie-rods which rigidly join each of saidbars to said horizontal beams or, in cases when the electricprecipitator consists of a number of groups or packages of emissionelectrodes and precipitation electrodes situated at intervals one afterthe other in the direction of flow of the gas, and associated impactdevices, also join a bar in a forward group to a bar in a rear-wardgroup in the direction of flow of the gas.

The invention will now be described with reference to the attacheddrawings, where FIG. I shows a cross-section through an electricprecipitator which horizontal gas flow and with dust traps forcollection and removal of precipitated dust,

FIG. 2 shows in enlargement a horizontal crosssection through a part ofthe electric precipitator with one embodiment of the linking deviceaccording to the invention,

FIG. 3 shows a longitudinal section through the same portion of theelectric precipitator as taken on the line 3-3 of FIG. 2,

FIG. 4 shows in enlargment a horizonal cross-section through a part ofthe electric precipitator with a different embodiment of the linkingdevice according to the invention.

FIG. 5 shows a longitudinal section through the same part of theelectric precipitator as FIG. 4.

In the drawing 1 denotes an electric precipitator for 7 horizontal flowin the direction of the arrow 2 of the gas to be cleaned, which entersat 18 and is visualized as leaving the electric precipitator at 20. Anumber of parallel rows of precipitation electrodes 4 are denoted 3. Inall cases of guidance and linkage shown, the precipitation electrodeshave a plane mid-portion 14 and partially bent-back fore and rearside-edges l2 and 13 respectively, viewed in the direction of flow ofthe gas, the which side-edges serve to stiffen the precipitationelectrodes, which are often of considerable length, 10-12 m, and extendthroughout the entire height of the electric precipitator. The emissionelectrodes 5 of the electric precipitator consist in the case shown ofso called spiral electrodes of the same length as the precipitationelectrodes and suspended in the conventional manner, electricallyinsulated from the precipita tion electrodes. The emission electrodesare supplied with a high voltage in the known manner. The impact device6 consists of a hammer of conventional type and is driven in the knownmanner at specific intervals against an impact rod 19 fitted to thebottom of the precipitation electrode. The parallel rows 3 of theprecipitation electrodes are situated between a number of transvers bars7 extending across the precipitator at different heights andperpendicular to the planes through the rows of precipitation electrodes4. The bars 7 have guides 8 opposite the ends of each row of electrodes4.

The precipitation electrodes are assumed to be linked together by meansof tongues 9 inserted in a rear bent-back side-edge 13 of aprecipitation electrode, and preferentially fixed to it, and a forebent-back sideedge 12 of the next precipitation electrode, with whichthe tongues preferentially have a clearance fit. Another type of linkageelement may consist of a E-shapcd strap 10 (FIG. 2). All precipitationelectrodes in one row may also as shown in FIG. 4 be anchored or linkedto one another by means of a continuous long and narrow, flat metal band9' (placed on edge). The band is assumed to pass both through the forebentback side-edge l2 and through the rear bent-back sideedge 13. Theband 9 allows in itself a small lateral movement of each of the linkedtogether precipitation electrodes and is preferentially fixed at 8' toone of aforesaid bars 7 at the beginning of each group of electrodesviewed in the direction of flow of the gas and at the end of the groupas indicated at 8"- passes through a nonthreaded opening 15 in the otherbar, between which bars the band 9' extends in one piece.

By giving each of the tongues 9 linking together the precipitationelectrodes 4 a bent-up lip |at one end, a limited reciprocal movement issimply and effectively arranged, at the same time preventing exceedingof said movement and an involuntary separation of two adjacentprecipitation electrodes. Were this to occur by mishap, the consequencewould be tripping and stoppage of operation.

To limit correspondingly the reciprocal movement of the precipitationelectrodes 4 when using the band 9, according to an effectiveembodiment, the latter can be provided with a number of invertedcastellated cutouts, e.g., of type FIE-11, along one edge resting in thelower edge of the nonthreaded opening.

Electric precipitators of the size in question should, on mechanicalgrounds, be provided with a number of horizontal beams 16 holdingtogether the sidewalls. As shown in the drawings, these are used tocarry tie-rods 17 which rigidly join together each of said bars 7 withsaid horizontal beams. If the electric precipitator consists of a numberof groups or packages of emission electrodes 5 and precipitationelectrodes 4 situated at intervals'in the direction of flow of the gas,such tierods 17 also join a bar in a forward group to a bar in arearward group (package) in the direction of the flow of the gas. Insome cases, in electric precipitators of very large dimensions, theaforesaid bars 7 are replaced by heavy beams 8a and 8b, as appears fromFIG. 5. 21 is a dust trap into which the matter precipitated by means ofthe electrostatic field on the precipitation electrodes 4 runs down andis carried off in an environmentally hygienic manner by means of a screwconveyor or the like not shown in the drawing. In other respects aswell, individual details and the form of the elements in the device maybe varied within the scope of the following claims.

What is claimed is:

I. In an electric precipitator designed for horizontal flow of the gasto be cleaned, and having plane precipitation electrodes placededge-to-edge in a number of rows parallel to the direction of flow ofthe gas through the electric precipitator, emission electrodes situatedbetween the rows, and an impact device displacing said electrodesparallel to the flow direction for cleaning of the precipitationelectrodes at specific intervals, the improvement wherein theprecipitator has a number of transverse bars fixedly mounted atdifferent heights extending perpendicular to the planes through the saidrows of precipitation electrodes adjacent the entrance and exit ends ofsaid rows, guides on each bar engaging the end electrodes in each row ofprecipitation electrodes to limit perpendicular movement thereof, and

linking elements for the precipitation electrodes in each row linkingthe electrodes together in the direction of impact along the plane ofeach row.

2. An improvement according to claim 1 wherein each precipitationelectrode has a fore and rear sideedge partially bent back in thedirection of flow of the gas for stiffening the electrode and a planeintermediate portion, and said linking elements comprise tongues securedin a rear, bent-back side-edge and entering into a fore, bent-backside-edge of the next precipitation electrode.

3. An improvement according to claim 2, characterized in that eachtongue has a bent-up lip to permit a limited reciprocal movementlongitudinally but at the same time to limit said movement and thusprevent involuntary separation of two adjacent precipitation electrodesfrom one another.

4. An improvement according to claim 1, characterized in that saidprecipitation electrodes have fore and rear bent-back side-edges, andsaid guides and linking elements each comprise a continuous long andnarrow, flat metal band passing both through the fore and rear bent-backside-edges of each precipitation electrodes, the band being at one endfixed to one of said bars and at the other end passing through the otherof said bars in a clearance hole,

5. An improvement according to claim 4, characterized in that the bandhas a number of cut-outs or notches along one edge resting in the loweredge of the clearance hole, the which cut-outs or notches permit alimited reciprocal movement but at the same time limit said movement andprevent separation of two adjacent precipitation electrodes from oneanother.

6. An improvement according to claim 1, characterized in that saidprecipitation electrodes have fore and rear bent-back side-edges, and atleast one of said linking elements comprises a |:-shaped strap attachedto the rear bent-back side-edge and embracing the fore bent-backside-edge of the next precipitation electrode, and in that the bent-backside-edge at the entrance end and the bent-back side-edge at the exitend in each row viewed in the direction of flow of the gas are fixedlateraly to said bars by means of said guides, and wherein each of saidguides comprises a [I -shaped or :I-shaped strap attached to itsassociated transverse bar.

7. An improvement according to claim 1 wherein the precipitator includeshorizontal beams holding together the side walls of the electricprecipitator and tierods which rigidly join each of said transverse barsto said horizontal beams.

8. An improvement according to claim 7 wherein the precipitator consistsof a plurality of groups of electrode rows spaced-apart in the directionof flow, said beams being disposed in the space between said groups,each beam supporting both the exit-end transverse bar of the fore groupand the entrance-end transverse bar of the rear group to join the same.

9. An improvement according to claim 1 wherein said linking elements aredisposed at the same heights the plane of said row.

1. In an electric precipitator designed for horizontal flow of the gasto be cleaned, and having plane precipitation electrodes placededge-to-edge in a number of rows parallel to the direction of flow ofthe gas through the electric precipitator, emission electrodes situatedbetween the rows, and an impact device displacing said electrodesparallel to the flow direction for cleaning of the precipitationelectrodes at specific intervals, the improvement wherein theprecipitator has a number of transverse bars fixedly mounted atdifferent heights extending perpendicular to the planes through the saidrows of precipitation electrodes adjacent the entrance and exit ends ofsaid rows, guides on each bar engaging the end electrodes in each row ofprecipitation electrodes to limit perpendicular movement thereof, andlinking elements for the precipitation electrodes in each row linkingthe electrodes together in the direction of impact along the plane ofeach row.
 2. An improvement according to claim 1 wherein eachprecipitation electrode has a fore and rear side-edge partially bentback in the direction of flow of the gas for stiffening the electrodeand a plane intermediAte portion, and said linking elements comprisetongues secured in a rear, bent-back side-edge and entering into a fore,bent-back side-edge of the next precipitation electrode.
 3. Animprovement according to claim 2, characterized in that each tongue hasa bent-up lip to permit a limited reciprocal movement longitudinally butat the same time to limit said movement and thus prevent involuntaryseparation of two adjacent precipitation electrodes from one another. 4.An improvement according to claim 1, characterized in that saidprecipitation electrodes have fore and rear bent-back side-edges, andsaid guides and linking elements each comprise a continuous long andnarrow, flat metal band passing both through the fore and rear bent-backside-edges of each precipitation electrodes, the band being at one endfixed to one of said bars and at the other end passing through the otherof said bars in a clearance hole.
 5. An improvement according to claim4, characterized in that the band has a number of cut-outs or notchesalong one edge resting in the lower edge of the clearance hole, thewhich cut-outs or notches permit a limited reciprocal movement but atthe same time limit said movement and prevent separation of two adjacentprecipitation electrodes from one another.
 6. An improvement accordingto claim 1, characterized in that said precipitation electrodes havefore and rear bent-back side-edges, and at least one of said linkingelements comprises a -shaped strap attached to the rear bent-backside-edge and embracing the fore bent-back side-edge of the nextprecipitation electrode, and in that the bent-back side-edge at theentrance end and the bent-back side-edge at the exit end in each row-viewed in the direction of flow of the gas - are fixed lateraly to saidbars by means of said guides, and wherein each of said guides comprisesa -shaped or -shaped strap attached to its associated transverse bar. 7.An improvement according to claim 1 wherein the precipitator includeshorizontal beams holding together the side walls of the electricprecipitator and tie-rods which rigidly join each of said transversebars to said horizontal beams.
 8. An improvement according to claim 7wherein the precipitator consists of a plurality of groups of electroderows spaced-apart in the direction of flow, said beams being disposed inthe space between said groups, each beam supporting both the exit-endtransverse bar of the fore group and the entrance-end transverse bar ofthe rear group to join the same.
 9. An improvement according to claim 1wherein said linking elements are disposed at the same heights as thetransverse bars to limit movement of each electrode in the row againstmovement perpendicular to the plane of said row.